Back button for conversation activity.

res/drawable/conversation_home_touch_highlight.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ripple xmlns:android="http://schemas.android.com/apk/res/android"
+    android:color="?attr/colorControlHighlight">
+    <!-- Add half of the medium_profile_picture_size padding on the right to better work with the group icons. -->
+    <item
+        android:id="@android:id/mask"
+        android:right="24dp">
+        <shape>
+            <corners
+                android:bottomLeftRadius="@dimen/medium_profile_picture_size"
+                android:topLeftRadius="@dimen/medium_profile_picture_size" />
+            <solid android:color="@android:color/white" />
+        </shape>
+    </item>
+</ripple>

res/drawable/ic_baseline_arrow_back_compact_24.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="?attr/colorControlNormal">
+  <path
+      android:fillColor="@android:color/white"
+      android:pathData="M11.67,3.87L9.9,2.1 0,12l9.9,9.9 1.77,-1.77L3.54,12z"/>
+</vector>

res/layout/conversation_activity.xml

@@ -11,19 +11,47 @@
         android:id="@+id/toolbar"
         android:layout_width="match_parent"
         android:layout_height="?attr/actionBarSize"
+        android:clipChildren="false"
+        android:contentInsetLeft="24dp"
+        android:contentInsetStart="24dp"
         app:contentInsetLeft="24dp"
-        app:contentInsetRight="20dp">
+        app:contentInsetStart="24dp"
+        android:contentInsetRight="20dp"
+        android:contentInsetEnd="20dp"
+        app:contentInsetRight="20dp"
+        app:contentInsetEnd="20dp">
 
         <LinearLayout
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             android:gravity="center_vertical"
-            android:orientation="horizontal">
+            android:orientation="horizontal"
+            android:clipChildren="false">
 
-            <org.thoughtcrime.securesms.loki.views.ProfilePictureView
+            <LinearLayout
-                android:id="@+id/profilePictureView"
+                android:id="@+id/homeButtonContainer"
-                android:layout_width="@dimen/medium_profile_picture_size"
+                android:layout_width="wrap_content"
-                android:layout_height="@dimen/medium_profile_picture_size" />
+                android:layout_height="wrap_content"
+                android:gravity="center_vertical"
+                android:orientation="horizontal"
+                android:background="@drawable/conversation_home_touch_highlight"
+                android:clickable="true"
+                android:focusable="true"
+                android:layout_marginLeft="-24dp">
+
+                <ImageView
+                    android:layout_width="18dp"
+                    android:layout_height="18dp"
+                    android:src="@drawable/ic_baseline_arrow_back_compact_24"
+                    android:layout_marginRight="-2dp"
+                    android:layout_marginLeft="8dp"/>
+
+                <org.thoughtcrime.securesms.loki.views.ProfilePictureView
+                    android:id="@+id/profilePictureView"
+                    android:layout_width="@dimen/medium_profile_picture_size"
+                    android:layout_height="@dimen/medium_profile_picture_size" />
+
+            </LinearLayout>
 
             <LinearLayout
                 android:layout_width="wrap_content"

src/org/thoughtcrime/securesms/conversation/ConversationActivity.java

@@ -323,6 +323,7 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
   private   ProgressBar                 messageStatusProgressBar;
   private   ImageView                   muteIndicatorImageView;
   private   TextView                    subtitleTextView;
+  private   View                        homeButtonContainer;
 
   private   AttachmentTypeSelector attachmentTypeSelector;
   private   AttachmentManager      attachmentManager;
@@ -1690,6 +1691,7 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
     messageStatusProgressBar               = ViewUtil.findById(this, R.id.messageStatusProgressBar);
     muteIndicatorImageView                 = ViewUtil.findById(this, R.id.muteIndicatorImageView);
     subtitleTextView                       = ViewUtil.findById(this, R.id.subtitleTextView);
+    homeButtonContainer                    = ViewUtil.findById(this, R.id.homeButtonContainer);
 
     ImageButton quickCameraToggle      = ViewUtil.findById(this, R.id.quick_camera_toggle);
     ImageButton inlineAttachmentButton = ViewUtil.findById(this, R.id.inline_attachment_button);
@@ -1744,6 +1746,8 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
     searchNav.setEventListener(this);
 
     inlineAttachmentButton.setOnClickListener(v -> handleAddAttachment());
+
+    homeButtonContainer.setOnClickListener(v -> onSupportNavigateUp());
   }
 
   protected void initializeActionBar() {